Enhancement of nitrogen removal in a modified dephanox process

A conventional DEPHANOX process was modified in order to improve the nitrogen removal efficiency. The modified-DEPHANOX was created by adding an extra intermittent aeration reactor in the process while reducing the size of the reaeration reactor. With respect to nitrification, it was observed that the nitrification performances of both processes were significantly affected by the nitrification efficiency in its respective nitrification reactors. Also, the increase of organic matters and ammonia loading rates in the nitrification reactors decreased the ammonia removal efficiency. In nitrification reactors, when the hydraulic retention times (HRT) were set at 8 and 6 h, and the temperature was set at 25°C, the increase in organic matter did not significantly affect nitrification. However, when they were set at 6 and 5 h and the temperature was set at 16 and 17°C, respectively, the increase in organic matter had a significant effect on nitrification. A comparative study of denitrification performance between DEPHANOX and M-DEPHANOX indicated that M-DEPHANOX was better than DEPHANOX in all experimental conditions. The superiority of M-DEPHANOX on denitrification was verified by PASS® software simulations. It was further observed that M-DEPHANOX had a higher phosphorus removal efficiency than DEPHANOX because its higher denitrification subsequently led to a lower NOx-N concentration in effluent (and thus lowered the recycle nitrate).